Copper rods and wires have been used as electrical conductors in various fields. For example, copper rods and wires have been used in the wire harnesses of cars, and the weights of the cars need to be reduced to improve fuel efficiency to counter global warming. However, the weights of the wire harnesses used tend to increase along with developments in car information, electronics, and hybridization. Since copper is expensive metal, the car manufacturing industry wants to reduce the amount of copper to be used in view of the cost. For this reason, when using a copper wire having high strength, high conductivity, bending resistance, and excellent ductility for a wire harness, it is possible to reduce the amount of copper used and thus it is possible to reduce the size and weight of cars. As described above, the invention of a high strength and high conductivity rod or wire has been made in response to contemporary needs.
There are several kinds of wire harnesses, such as a power system and a signal system in which very little current flows. For the former, conductivity close to that of pure copper is required as the first priority. For the latter, high strength is especially required. Accordingly, a copper wire balanced in strength and conductivity is necessary depending on its purpose. Power distribution lines and the like for robots and airplanes are required to have high strength, high conductivity, and bending resistance. In such power distribution lines, there are many cases where copper wire is used as a stranded wire including several or several tens of thin wires in a structure in order to further improve bending resistance. In addition, copper rods used for welding tips are required to have high strength and high conductivity. In this specification, a wire means a product having a diameter or an opposite side distance of less than 6 mm. Even when the wire is cut in a rod shape, the cut wire is called a wire. The term rod refers to a product having a diameter or an opposite side distance of 6 mm or more. Even when the rod is formed in a coil shape, the coil-shaped rod is called a rod. Generally, material having a large outer diameter is cut in a rod shape, and thin material is formed into a coil-shaped product. However, the material can be referred to both as a wire and a rod when a diameter or an opposite side distance is 4 to 16 mm. Accordingly, the aforesaid definition was made herein. A collective term for a rod and a wire is also defined as a rod wire.
A high strength and high conductivity copper rod or wire (hereinafter, referred to as a high performance copper rod or wire) according to the invention requires the following characteristics according to applications:
A wire has become thinner on the male side of a connector cable and a bus bar along with any reduction in connector size, and thus strength and conductivity capable of withstanding the putting-in and taking-out of the connector is required. Since temperature rises while in use, a stress relief resistance is also necessary.
For a wire used as wire cutting (to discharge), high conductivity, high strength, wear resistance, high-temperature strength, and durability are required.
For a trolley line, high conductivity and high strength are required, and durability, wear resistance, and high-temperature strength are also required during use. Generally, such a trolley line is called a trolley “wire”. However, since there are many trolley lines having a diameter of 20 mm, the trolley lines in fact fall within the scope of “rod” in this specification.
For a welding tip, high conductivity, high strength, wear resistance, high-temperature strength, and durability are required.
Electrical components, for example, bus bars, rotor bars, terminals, electrodes, relays, power relays, connectors, connection terminals, fixers, and the like, are required to have high conductivity and high strength. In addition, mechanical components such as the nuts and fittings of faucets are produced from rods by cutting, pressing, or forging, and thus are required to have high conductivity, high strength, and wear resistance. There are many cases where, from the viewpoint of bonding part reliability, brazing is used as a bonding means for faucets, electrical components such as rotor bars used in motors, or power relays, and thus heat resistance for keeping high strength even after high-temperature heating at, for example, 700° C. is necessary. Heat resistance in this specification means that recrystallization does not occur easily even by heating at a temperature of 500° C. or higher and that strength after heating is excellent.
For mechanical components or faucet fittings, a pressing process and a forging process are performed followed by a downstream process includes rolling and partial cutting. Particularly, formability in cold temperatures, ease of forming, high strength, and wear resistance are necessary, and it is required that there is no stress corrosion cracking.
A continuous casting and rolling method for producing a copper rod or wire provides high productivity and low costs. Generally, trapezoid, polygonal, oval, and cylindrical casting rods having a side of several tens millimeters (sectional area is 1000 to 9000 mm2, generally about 4000 mm2) obtained by melting and casting are continuously hot rolled (processing rate of 70 to 99.5%) by 8 to 20 rolling rollers after casting, thereby obtaining rods having circular, oval, polygonal shapes, and the like in the sectional view with a sectional area of 35 to 700 mm2 (generally 100 mm2).
In addition, these rods are drawn out by a drawing process to become thinner and are made into wire by a wire drawing process (the general term for the drawing process for drawing out the rods and the wire drawing process for drawing out the wires is referred to as the drawing/wire drawing process). Bus bars, polygonal rods, or rods having complicated shapes in the sectional view are made from the rods by a kind of extruding (generally referred to as conforming). Basically, in the continuous casting and rolling method, deformation resistance is low in the high temperature range encountered at the time of hot rolling, and the method is used as a method for producing materials for pure copper cables with excellent hot deformability immediately after solidification. However, when alloy elements are added to pure copper, hot deformation resistance becomes high and thus deformability becomes low. Particularly, the addition of elements increases the solidification temperature range, and the solidus temperature becomes low. Accordingly, copper alloy is unsuitable for the continuous casting and rolling process which requires excellent deformability immediately after solidification. That is, in order to make a copper alloy rod or wire by the continuous casting and rolling process, it is necessary that hot deformation resistance should be low and hot deformability be excellent immediately after solidification.
A copper rod or wire, which contains 0.15 to 0.8 mass % of Sn and In in total with the remainder including Cu and inevitable impurities, has been known (e.g., Japanese Patent Application Laid-Open No. 2004-137551). However, the strength of such a copper rod or wire is insufficient. In addition, a continuous casting and rolling process is not performed, but a casting process and a rolling process are performed separately, resulting in high costs.